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ignition project for old car/motorcycle enthusiasts

Discussion in 'Electronic Design' started by kell, Jul 18, 2005.

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  1. kell

    kell Guest

    simple "ignition amplifier" circuit for use on old vehicle with points

    12 volts switched
    | |
    | |
    / / to coil negative
    \ \ |
    /56k 2.2k / |
    \ \ ___|c
    | | |
    | ___|____| | igbt
    | c/ g |___
    | / |e
    | | |
    |______/\/\/\_______| |
    | 2.2k | |
    | \ |
    | e\ |
    to points | |
    | |

    You should use an ignition coil driver igbt like the hgtp14n40f3vl or
    the mgp(Iforgettherest). Just go to Digikey and type in mgp, it will
    come up. If you wanted to use a mosfet you would need a 400 volt
    rating and a fairly low resistance (like a quarter ohm), and preferably
    an avalanche rating, which means spendy and the mosfet won't have the
    clamping protections the coil driver igbt has. So just use a coil
    driver igbt. You can go with less than 2.2k on the resistors if you
    use half watt resistors.
    Now I expect some criticism of this circuit from the pros on the NG,
    but I've built some and sold them to guys on an antique motorcycle BB
    over the last few years, no complaints. I use this circuit on my 1973
    International Harvester Scout II and my 1952 Harley.
    With this circuit you can use less resistance in the coil primary
    circuit -- more zap! For example on the Scout, I don't use a ballast
    resistor; only the stock coil, which has a little over 1.5 ohms primary
    resistance. As you can guess, the power transistor needs heat sinking.
    You will never have to file your points or replace them. You don't
    need a condenser with the ignition amplifier. (In fact you have to
    disconnect the condenser.)
  2. snip

    I'd think that reducing the 56K resistor substantially would make
    it more reliable, the points are made for amps of current might
    not keep clean with only a few hundred microamps running through them.

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